JPH0751809A - Production of corrosion resistant and heat resistant super alloy thin sheet - Google Patents

Abstract

PURPOSE:To achieve the saving of equipment, energy and labor by specifying press-contact load at the time of continuously casting a corrosion resistant and heat resistant super alloy having specific component composition. CONSTITUTION:The composition of the corrosion resistant and heat resistant super alloy is made to be by mass% 50-55% Ni, 17-22% Cr, 2.8-3.3% Mo, 0.2-0.8% Al, 0.65-1.15% Ti, 4.75-5.50% Nb+Ta and the balance Fe with inevitable impurities. At the time of casting this molten alloy produced with a vacuum induction furnace, the casting is executed with a twin roll type continuos caster provided with an inner part water-cooled roll sleeve made of copper, etc., having reverse crown shape at the room temp. in order to keep the roll gap constant at the time of developing the heat expansion to produce a thin sheet. The press-contact load P at the time of executing the continuous casting is made to satisfy the inequality 1.4r<1/2>.b<=P<=5.7r<1/2>.b. Wherein, P: pressure- contact load (KN), r: roll radius at the initial stage (mm), b: sheet width (mm). By this method, the thin sheet without lamination fault and bulging defect can be obtd.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention is 50 to 55 mass%.
Ni, 17-21 mass% Cr, 2.8-3.3 m
ass% Mo, 0.2-0.8mass% Al, 0.0.
65 to 1.15 mass% Ti, 4.75 to 5.50 m
A method for producing a corrosion-resistant, heat-resistant superalloy sheet containing ass% of Nb + Ta and the balance of Fe and unavoidable impurities, and particularly, a corrosion-resistant, heat-resistant superalloy sheet having a sound internal quality with no defects of double cracks. The present invention relates to a manufacturing method of.

[0002]

2. Description of the Related Art 50-55 mass% Ni, 17-2
1 mass% of Cr, 2.8 to 3.3 mass% of Mo,
Al of 0.2-0.8 mass, 0.65-1.15 mass
s% Ti, 4.75 to 5.50 mass% Nb + Ta
An alloy containing Ni and the balance of Fe and unavoidable impurities (hereinafter referred to as "this alloy") is a JIS standard NCF.
It is widely known industrially as a corrosion-resistant heat-resistant superalloy specified in 718. Since this alloy has excellent strength and oxidation resistance especially at high temperatures, it has been used for special applications such as jet engine parts and parts for nuclear reactors, and recently it has been widely used for automobile parts and electronic device parts materials. Has been done.

Conventionally, the following methods have been known for manufacturing a thin plate of the present alloy. 1. A method of repeatedly hot rolling an ingot obtained by melting and casting an alloy having the above composition in a vacuum induction furnace and solidifying the alloy to obtain a hot rolled sheet having a desired thickness. 2. The alloy having the above composition is melted and cast in a vacuum induction furnace, and the ingot obtained by solidifying is used as an electrode, and is further melted and solidified in a vacuum arc melting furnace to produce an ingot, which is then forged. A method of repeatedly performing hot rolling until a hot rolled sheet having a desired thickness is obtained.

[0004]

However, while this alloy has high strength at high temperatures, it has the property of being extremely poor in hot workability due to its large deformation resistance at high temperatures.
In addition, since coarse alloys and Laves phase are easily generated in the present alloy due to segregation in the final stage of solidification, embrittlement occurs and cracks easily occur during hot rolling. Therefore, there is a problem that the reduction ratio when hot rolling this alloy cannot be increased and the temperature range in which rolling is possible is narrow.

Therefore, in order to obtain a thin plate from the ingot of the present alloy by the above-mentioned conventional manufacturing method, hot rolling must be repeated a considerable number of times with a small reduction, and the material temperature during rolling must be increased. Since rolling becomes difficult when the temperature decreases, it was necessary to put the material into the heating furnace and heat it at a fixed number of rollings. Therefore, the conventional manufacturing method requires a remarkably large number of steps and a large amount of energy, resulting in a high manufacturing cost.

The twin roll method is also known as a means for directly obtaining a thin plate from a molten metal. However, like the present alloy, a corrosion resistant heat resistant superalloy having a difference between the liquidus temperature and the solidus temperature of 150 K or more. Regarding the above, when the conventional twin roll method is applied as it is to continuously cast thin plates, there is a problem that large thin cracks and bulging are likely to occur in the center of thickness of the obtained thin plates, and healthy thin plates cannot be manufactured stably. there were.

The present invention provides a method for directly manufacturing a thin plate from a molten metal by continuously casting a corrosion-resistant heat-resistant superalloy as defined by JIS NCF718.
The purpose is to omit the forging and hot rolling processes and to significantly reduce the process and cost.

[0008]

In order to achieve the above object, Ni: 50 to 55 mass%, Cr: 17 to 21 m
ass%, Mo: 2.8 to 3.3 mass%, Al: 0.
2 to 0.8%, Ti: 0.65 to 1.15 mass%, N
b + Ta: 4.75 to 5.50 mass% is contained, the balance is a melt of a corrosion-resistant heat-resistant superalloy having a composition of Fe and unavoidable impurities, and the melt is melted in a vacuum induction furnace. In the twin roll continuous casting machine equipped with an internal water-cooled roll sleeve made of copper or copper alloy, which has an inverted crown shape at room temperature so that the roll gap becomes constant in the width direction when thermally expanded in The crimping load P during continuous casting is 1.4r ^1/2 · b ≦ P ≦ 5.7r ^1/2 · b P: crimping load (kN) r: initial roll radius ( mm) b: A method for producing a corrosion-resistant, heat-resistant superalloy thin plate controlled to satisfy a plate width (mm).

[0009]

The present inventors first investigated the quality of the thin plate obtained by casting various Ni-based alloys by the twin roll method.
As a result, when a thin plate of a corrosion-resistant heat-resistant superalloy containing a large amount of components such as Nb, Mo, and Ti with a high segregation coefficient is directly produced from the molten metal by the twin roll method, the surface of the obtained thin plate randomly bulges. I understood. Then, when the cross section at the bulged position was examined, so-called two-piece cracking in which the upper shell and the lower shell were not joined was observed at the center of the plate thickness.

Therefore, the liquidus temperature and the solidus temperature of the alloy having such two cracks are determined by DTA (differential thermal analyzer).
The temperature difference between the liquidus line and the solidus line was 150 K or more, and a peak corresponding to the eutectic reaction was observed at the end of solidification.

[0011] Here, in hot rolling, crocodile cracking has been reported as a phenomenon similar to double cracking [Lecture / Modern Metallurgy: Material deviation 11 Metalworking: Japan Institute of Metals (19)
86) p192], this report explains that crocodile cracks occur as a result of tensile stress acting in the thickness direction when the center part of the plate thickness with low deformation resistance is preferentially deformed when rolled by a roll. ing. The double cracks in thin plate continuous casting do not open like the crocodile cracks in hot rolling but are scattered in the inside of the plate, but it is speculated from the morphology that they are caused by the same mechanism as crocodile cracks.

And, Nb, Mo, Ti having a high segregation coefficient
For alloys containing a large amount of such components, it is easy for double cracking to occur because component segregation occurs in the final solidification part and the concentrated molten metal tends to remain in the form of a film at the center of the plate thickness even near the roll kiss point. It is considered that this is because the joint surface of each solidified shell that has grown from both sides has no ductility and the joint strength is small. An alloy such as NCF718, which is the object of the present invention, is particularly susceptible to double cracking among corrosion-resistant heat-resistant superalloys.

On the other hand, if the pressure-bonding load is reduced so that the two sheets are not cracked, bulging tends to occur. That is,
In the region where the growth of the solidified shell from both roll surfaces is the slowest when the crimping load is small, it is presumed that unsolidified molten steel is still present in the center of the plate thickness even after the plate is detached from the rolls, causing bulging due to reheat. To be done.

Therefore, next, the present alloy is cast by using a twin roll type thin plate continuous casting machine equipped with rolls having a constant radius (flat) in the width direction at room temperature. At that time, the plate just below the roll kiss point is cast. By continuously measuring the surface temperature by thermography, we investigated the relationship between the temperature unevenness on the plate surface and the locations of bulging and cracking. As a result, as described above, a roll with a constant radius in the width direction at room temperature deforms and expands into a crown shape (the center of the roll bulges into a barrel shape) due to uneven thermal expansion during casting, and The diameter becomes the largest, and due to this, a large reduction occurs locally at the widthwise center of the thin plate.
As shown in Fig. 5, the central part in the plate width direction was the strong cooling part with the lowest plate surface temperature. Then, the two-sheet crack occurred in the strong cooling part.

On the other hand, since the diameter of the roll end portion becomes smaller than the diameter of the central portion due to thermal expansion, the reduction of the widthwise both ends of the thin plate is relatively small, and the plate near both ends of the thin plate is relatively small. The surface temperature became high as a whole, and as shown in Fig. 2, bulging occurred in the slow cooling part where the temperature was particularly high near both ends of the thin plate with small reduction.

Next, the present alloy was cast by the twin roll method using a twin roll type continuous casting machine equipped with roll sleeves of 1 to 3 as shown below. The relationship between the occurrence frequency of bulging and the crimping load was investigated. 1. With a constant radius in the width direction at room temperature (flat),
1. Internal water-cooled roll sleeve made of steel With a constant radius in the width direction at room temperature (flat),
2. Internal water-cooled roll sleeve made of copper alloy An internal water-cooled roll sleeve made of copper alloy and having an inverted crown shape at room temperature so that the roll gap becomes constant in the width direction when thermally expanded during the steady-state heat during casting. 20 in the center
It was 0 mm, and the obtained plate width was 300 mm.

As a result, the results shown in FIG. 3 were obtained. That is, as a whole, the higher the crimping load, the higher the frequency of occurrence of two-piece cracks, and if the crimping load is excessively reduced, the frequency of bulging increases, which is similar to the previous result. On the other hand, when viewed relatively, "3. Internal water-cooled roll sleeve made of copper alloy, which has an inverted crown shape at room temperature so that the roll gap is constant in the width direction when thermally expanded in the thermal steady state during casting" When a thin plate is cast by a twin roll type continuous casting machine equipped with a
In contrast to 718, in order to stably obtain a thin plate having no two cracks and no bulging defect, in the case of the roll, the crimping load during casting should be controlled within the range of 6 kN or more and 24 kN or less. I found out.

From the above results, an inner water-cooled roll sleeve made of copper or copper alloy having an inverted crown shape at room temperature so that the roll gap is kept constant in the width direction when thermally expanded in a thermal steady state during casting is obtained. The twin roll type continuous casting machine provided was used for continuous casting to produce a thin plate.

As a roll material, a precipitation hardening type copper alloy having a high thermal conductivity, a high hardness and an excellent wear resistance is practical. Further, in order to further reduce the wear amount, Ni or Ni + Fe plating having a thickness of 2 mm or less may be applied to the roll surface.

The pressure load during casting is 6 kN when the roll radius is 200 mm and the plate width is 300 mm.
As described above, the range may be controlled to 24 kN or less, but this range varies depending on the roll diameter and the plate width. Here, the rolling load P in rolling is represented by the following formula (1). P = km * ld * b ... (1) Here, km: average deformation resistance ld: contact length b: board width And contact length ld is shown by the following (2) Formula. ld = (rΔh) ^1/2 (2) where r: roll radius Δh: reduction amount Therefore, the following equation (3) can be obtained from equations (1) and (2). P = km · (r · Δh) ^1/2 · b (3)

In the twin roll method, km · (Δh) ^1/2 is unknown, but as shown in the results of the above investigation, a twin roll experimental apparatus equipped with a roll having a radius (r) of 200 mm was used. When a plate width (b) 300 mm casting experiment was performed, the lower limit value of the proper crimping load was 6 kN and the upper limit value was 24 kN. In case of: km · (△ h) ^1/2 = 1.4
(N / mm ^3/2 ) Upper limit value (24 kN): km · (Δh) ^1/2 = 5.7
(N / mm ^3/2 ).

According to the present invention, however, when casting NCF 718 having a plate width b with a twin roll machine having a roll radius r, by controlling the crimping load P during casting within the following range, two-piece cracks occur. We decided to prevent the occurrence of bulging. 1.4r ^1/2・ b ≤ P ≤ 5.7r ^1/2・ b (4)

[0023]

EXAMPLES Examples of the present invention will be specifically described below. Table 1
The invention examples used in the examples (heat No. 1 to
6) and each comparative example (heat No. 7-9) and each investigation result are shown.

[0024]

[Table 1]

[Examples of the present invention: Heat Nos. 1 to 4] An inverse crown shape was formed at room temperature so that the roll gap was constant in the width direction when thermally expanded in a thermal steady state during casting.
Using a twin-roll type continuous casting machine equipped with a precipitation-hardened copper alloy internal water-cooled roll sleeve, 500 kg of NCF718 molten metal melted in a vacuum induction furnace was continuously cast at an average casting speed of 25 m / min. Cast. Roll radius is 2
An inverted crown-shaped roll sleeve having a radius of 00 mm and a radius of 0.1 mm larger at the end than at the center of the roll at room temperature and having a taper formed in the width direction was used. The roll diameter (at room temperature) was 20.0 mm at the center of the roll and 20.1 mm at the end of the roll. Effective roll length is 3
It was set to 00 mm. And heat No. 1, 2, 3, 4
, Thickness 1.5mm, 2.0mm, 2.4mm, 3.0
mm thin plates (each having a plate width of 300 mm) were manufactured.

The composition of each match money is Ni: 52 to 53 m
% ass, Cr: 19 to 20% by mass, Mo: 2.9
~ 3.0 mass%, Al: 0.45 to 0.70 mass
%, Ti: 0.85 to 1.05 mass%, Nb + Ta:
The balance of 4.95 to 5.10 mass% was Fe and inevitable impurities.

Then, as described above, the plate width (b) is 300 m.
Under conditions of m and roll radius (r) of 200 mm, control was performed by changing the casting speed so that the crimping load P during casting was 6 kN ≤ P ≤ 24 kN to satisfy the above formula (4). .

Heat Nos. 1 to 4 produced under the above conditions
The thin plate of (Example of the present invention) was examined by an ultrasonic flaw detector, and the cross section of the thin plate cut in the width direction was observed to examine two cracks. As shown in Table 1, in any case Also, no two-piece crack was observed except in the unsteady region in the early stage of casting. Moreover, neither bulging occurred.

[Inventive Example: Heat No. 5] Heat No.
Like Nos. 1 to 4, heat Nos. 1 to 4 were used by using a twin roll type continuous casting machine equipped with a reverse-crown-shaped precipitation-hardened copper alloy roll sleeve internally water-cooled at room temperature.
500kg alloy melt of the same composition as the average casting speed 36m
/ Min continuously cast. The roll radius is 30
The roll diameter (at room temperature) was 30.0 mm at the center of the roll and 300.1 mm at the end of the roll, and the effective barrel length was 300 mm. And thickness 2.0m
A thin plate having a plate width of 300 mm and a width of 300 mm was manufactured.

Then, as described above, the plate width (b) is 300 m.
Under conditions of m and roll radius (r) of 300 mm, the pressure-bonding load P during casting was controlled by changing the casting speed so as to satisfy 7kN ≤ P ≤ 30kN to satisfy the above formula (4). .

The heat No. 5 (inventive example) thin plate manufactured under the above conditions was examined by an ultrasonic flaw detector in the same manner as above, and two sections were observed by observing the cross section of the thin plate in the width direction. When the cracks were investigated, as shown in Table 1, two cracks were not observed except in the unsteady region at the initial stage of casting. Moreover, bulging did not occur.

[Invention Example: Heat No. 6] Heat No.
As in No. 5, using a twin-roll continuous casting machine with a reverse-crown-shaped precipitation hardening copper alloy roll sleeve internally cooled by water at room temperature, 500 kg of molten alloy with the same composition as Heat No. 5 Was continuously cast at an average casting speed of 36 m / min. The roll radius was 300 mm and the effective barrel length was 600 mm. The roll diameter (at normal temperature) is 300.0 mm at the center of the roll and 300.15 mm at the end of the roll, with a thickness of 2.0 mm and a plate width of 600.
mm sheets were produced.

As described above, the plate width (b) is 600 m
Under conditions of m and roll radius (r) of 300 mm, control was performed by changing the casting speed so that the pressure bonding load P during casting was 14 kN ≤ P ≤ 60 kN to satisfy the above formula (4). .

The thin plate of heat No. 6 (inventive example) manufactured under the above conditions was examined by an ultrasonic flaw detector in the same manner as above, and two sections were observed by observing the cross section of the thin plate cut in the width direction. When the cracks were investigated, as shown in Table 1, two cracks were not observed except in the unsteady region at the initial stage of casting. Moreover, bulging did not occur.

[Comparative Example-Heat No. 7] Using the same rolls as those used in Heat Nos. 1 to 4 of the present invention example, the crimping load, which was 18 kN (within the present invention range) at the beginning of casting, was changed from the middle. It was increased to 29 kN (the range exceeding the upper limit defined by the equation (4)), and in that state, the thin plate was continuously cast for about 10 m, and then was returned to 18 kN again. The molten metal composition and other casting conditions were the same as in Heat Nos. 1 to 4.

When the heat No. 7 (comparative example) thin plate produced under the above conditions was examined for two cracks by the same method, it was found that the width at the position corresponding to the time when the crimping load was increased to 29 kN. Two cracks of about 10 mm were observed almost continuously.

[Comparative Example-Heat No. 8] Using the same rolls as those used in Heat Nos. 1 to 4 of the present invention example, the crimping load which was 14 kN (within the present invention range) at the beginning of casting was changed from the middle. It was lowered to 4 kN (a range lower than the lower limit value defined by the equation (4)), and in that state, the thin plate was continuously cast for about 10 m and then returned to 14 kN again. The molten metal composition and other casting conditions were the same as in Heat Nos. 1 to 4.

In the thin plate of heat No. 8 (comparative example) manufactured under the above conditions, bulging was observed almost continuously at the position corresponding to the time when the pressure bonding load was reduced to 4 kN.

[Comparative Example-Heat No. 9] A flat diameter 400 at normal temperature without reverse crowning
mm, an effective cylinder length of 300 mm and a copper alloy roll sleeve were mounted on a casting machine for casting. The crimping load during casting is within the range of the crimping load obtained from the equation (4) 15 to
It was set to 22 kN.

With respect to the thin plate of heat No. 9 (comparative example) manufactured under the above-mentioned conditions, an inspection for two cracks was conducted by the same method as described above. Cracks were found.

[0041]

EFFECTS OF THE INVENTION According to the present invention, N, which is a hard-to-hot work material
The CF718 alloy can be directly cast from the molten metal to obtain a thin plate without double cracks or bulging defects. Therefore,
Significant equipment savings, energy savings, and labor savings are achieved in the production of thin sheets of this alloy.

[Brief description of drawings]

FIG. 1 is a drawing showing the distribution of the plate surface temperature of NCF718 alloy cast by a twin roll type thin plate continuous casting machine equipped with a flat roll sleeve at room temperature and the occurrence of double cracking.

FIG. 2 is a drawing showing the distribution of plate surface temperature and the occurrence of bulging of NCF718 alloy cast by a twin roll type thin plate continuous casting machine equipped with a flat roll sleeve at room temperature.

FIG. 3 is a graph showing the relationship between the crimping load and the frequency of occurrence of bulging and splitting of two sheets.

Claims (1)

[Claims] 1. Ni: 50 to 55 mass%, Cr: 17
-21 mass%, Mo: 2.8-3.3 mass%, A
1: 0.2 to 0.8%, Ti: 0.65 to 1.15 mass
%, Nb + Ta: 4.75 to 5.50 mass%, and the balance is a melt of a corrosion-resistant heat-resistant superalloy having a composition consisting of Fe and unavoidable impurities in a vacuum induction furnace. Continuous casting was performed by a twin roll type continuous casting machine equipped with an internal water-cooled roll sleeve made of copper or copper alloy, which was shaped like an inverted crown at room temperature so that the roll gap would be constant in the width direction when thermally expanded in a steady state. A thin plate is manufactured, and the crimping load P during continuous casting is 1.4r ^1/2・ b ≤ P ≤ 5.7r ^1/2・ b P: crimping load (kN) r: initial roll Radius (mm) b: A method for producing a corrosion-resistant heat-resistant superalloy thin plate controlled to satisfy a plate width (mm).